CINCINNATI (AP) — The Washington Nationals have put Stephen Strasburg on the 15-day disabled list, a day after he had to leave a start after 16 pitches because of a stiff neck.

Strasburg had a rough May, failing to last four innings in four of his five starts. He left one start with tightness behind his right shoulder.

The left side of his neck tightened after the first inning of a 5-2 loss to the Reds on Friday night, and he came out of the game after facing only one batter in the second inning.

Manager Matt Williams said on Saturday that the team wants to find out why he’s having back and neck problems. Right-hander Taylor Hill was called up from Triple-A Syracuse.